1. Field of the Invention
The present invention relates to a composition of conductive rubber used for a conductive member like a cord switch, etc.
2. Related Art
Generally, a type of a composition of conductive rubber of adding conductive additive like carbon, etc. into a base rubber is used as a composition of conductive rubber applied for electromagnetic shield, static elimination, electrodes of a pressure sensitive switch, etc. As such a conductive rubber, for example, acrylonitrile butadiene rubber (NBR) to which carbon is added for the conductive additive is proposed by e.g. Japanese Patent Laid-Open No. 7-126439 (JP-A 7-126439) and silicon rubber to which carbon is added is also proposed by e.g. Japanese Patent Laid-Open No. 10-30059 (JP-A 10-30059).
As methods for crosslinking the composition of conductive rubber, there are sulfur cross-linkage, peroxide cross-linkage, cross-linkage by electron beam radiation and the like. In the abovementioned methods, when a sheet, etc. are extruded to be molded, an extrusion process temperature should be set in a range that cross-linkage does not occur, because the sulfur cross-linkage or the peroxide cross-linkage occurs by thermal trigger.
On the other hand, the cross-linkage by electron beam radiation has a feature by which molding at a high temperature is capable, because the cross-linkage by electron beam radiation is performed by radiation of electron beam to a molded body so that the cross-linkage does not occur in an extrusion molding apparatus not to cause defective in shape.
Especially, when there is a need to reduce a volume resistance of a composition of conductive rubber, a large amount of conductive additive like carbon, etc. should be added to the composition of conductive rubber, so that the composition of conductive rubber becomes high in viscosity and bad in workability. For this reason, the cross-linkage by electron beam radiation, in which molding can be carried out even in a state of low viscosity at a high temperature, is effective for cross-linking the composition of conductive rubber which has a low volume resistance.
When the cross-linkage by the electron beam radiation is used for a cross-linkage method, the cross-linkage by the electron beam radiation is carried out in many cases at a separate stage after a metallic molding or an extrusion molding, etc. This is because a cross-linkage apparatus by electron beam radiation is very expensive and difficult to be set into those molding processes.
For this reason, when molded bodies such as uncross-linked sheets which are formed by metallic molding or extrusion molding, etc, are moved to a following stage for electron beam radiation cross-linkage, there is a case where the molded bodies are piled up or wound in many turns around a bobbin. However, there is a problem in which the molded bodies are adhered each other to be stuck one on another because of uncross-linkage of conductive rubber.